Electroosmotic Pumping in Unit Cells.

Electrodialysis in unit cells is described and analyzed in terms of the transport coefficients characterizing the membrane pairs. Bags made of three different types of cation- and anion-exchange membranes were used in actual experiments, namely, thin and thick polyethylene-based and Selemion membranes. Brine concentrations, volume flows, and current efficiencies were determined for different current densities, at a fixed value of the NaCl concentration of the feed. The graphs of brine concentration, c//b, vs. current density level off at high values of i, and c//b approaches a maximum plateau, c//b(max), which depends only on the electroosmotic coefficient of the membrane pair, c//b(max) equals one-half F beta . The smaller the ratio between osmotic and electroosmotic water flows, the smaller the current necessary to reach this plateau.